1. Field of the Invention
The present invention relates to methods for preparing a bismuth iodide article and for manufacturing a radiation detecting element.
2. Description of the Related Art
For medical practice and industrial application, radiation detectors have been studied which include a radiation detecting element including a conversion layer made of a heavy metal halide, such as lead iodide (PbI2), mercury iodide (HgI2) or bismuth iodide (BiI3). It is generally known that a conversion layer made of a heavy metal halide having a halogen defect has a low resistance and reduces signal current that will be detected by the radiation detecting element. The term signal current mentioned herein refers to the value obtained by subtracting the current value under a non-irradiation condition from the current value under an irradiation condition.
Japanese Patent Laid-Open No. 2005-327817 discloses a technique for reducing halogen defects by adding a halogen as well as a heavy metal halide to a detection layer so as to suppress the dissociation of the halogen from the heavy metal halide caused by X-ray irradiation. In addition, a process is disclosed of adding a halogen as well as the heavy metal halide to the detection layer by depositing lead iodide in iodine vapor.
It has been however found that when bismuth iodide is deposited in iodine vapor for forming a bismuth iodide detection layer, the deposition rate is considerably reduced because the deposition is performed under a high pressure produced by iodine vapor. Hence, it takes a long time to form a bismuth iodide layer having a thickness sufficient to absorb radiation.